The present invention relates to an electronic control device which electronically controls a control target.
A technique for achieving safety during vehicle traveling has been developed with improvement of an electronic control technique.
For example, if occurrence of skidding is detected during corner traveling on the basis of an output value from an angular velocity sensor, an electronic control device controls the fuel injection amount of the engine or the ignition timing and performs brake control to cause the vehicle to appropriately travel along the corner, thereby preventing the vehicle from being out of the traveling line and causing an accident. This function is called VSC (Vehicle Stability Control).
If collision of the vehicle is detected on the basis of an output value from an acceleration sensor, an airbag electronic control device initiates a squib to cause the airbag to inflate, thereby preventing a passenger from being injured due to collision.
An electronic control device which is a core element for such control has an electronic substrate, on which electronic components, such as a microcomputer and sensors, are mounted, and the like. As a representative electronic component mounted on the electronic substrate, an angular velocity sensor or an acceleration sensor is provided. A sensor in which the associated components are shared and unified is disclosed in Patent Document 1.
An electronic control device having such sensors is designed such that the frequency band of a signal for detection by each sensor does not overlap the resonance frequency of the electronic control device having an electronic substrate and a housing. If the frequency band of a signal for detection by the sensor overlaps the resonance frequency of the electronic control device, the electronic control device may erroneously determine rotation or collision of the vehicle on the basis of a sensor detection signal when resonance occurs in the electronic control device.
Patent Document 1: JP-A-2005-283424
However, the frequency band of a signal for use when the acceleration sensor detects collision of the vehicle differs from the frequency band of a signal for use when a yaw rate sensor detects rotation of the vehicle. For this reason, even when the electronic control device is designed such that the resonance frequency does not affect the frequency band which is used in one sensor, if the resonance frequency overlaps the frequency band which is used in the other sensor, a control section erroneously controls a control target. Hereinafter, this problem will be described in detail.
As shown in FIG. 1, an airbag electronic control device mounted in a vehicle includes an electronic substrate 6 on which electronic components, such as an arithmetic section 2, an acceleration sensor 3 detecting the acceleration of the vehicle, a connector 4 for signal input/output with respect to an external device, and a capacitor 5 capable of supplying accumulated charges to the electronic components mounted on the electronic substrate, and a housing which accommodates the electronic substrate 6 and is fixed to the body of the vehicle.
The airbag electronic control device 1 has a function to determine whether the vehicle is colliding or not on the basis of the acceleration detected by the acceleration sensor 3, and when it is determined that the vehicle is colliding, to initiate the squib so as to cause the airbag to inflate.
The acceleration sensor 3 uses a low frequency band equal to or lower than thousands of Hz at the time of detection. In this case, if the resonance frequency which is generated when vibration is applied from the outside to the airbag electronic control device 1 having the housing and the electronic substrate 6 overlaps the low frequency band to be used, resonance occurs due to vibration, not collision of the vehicle, thus the control section of the airbag electronic control device 1 may erroneously determine that the vehicle is colliding and cause the airbag to inflate.
Resonance with a low frequency does not occur in a hard material. Thus, screws are fastened to four fixing portions of the housing and the electronic substrate to tightly fix the housing and the electronic substrate, such that the frequency of occurring resonance further increases and is kept out of the use frequency band of the sensor, thereby preventing erroneous control. Hereinafter, such fixing is called four-point fixing.
Meanwhile, as shown in FIG. 2, a VSC electronic control device mounted in the vehicle includes an electronic substrate 25 on which electronic components, such as an arithmetic section 21, an angular velocity sensor 22 detecting the angular velocity of the vehicle, a connector 23 for signal input/output with respect to an external device, and a capacitor 24 capable of supplying accumulated charges to the electronic components mounted on the electronic substrate 25, are mounted, and a housing which accommodates the electronic substrate 25 and is fixed to the body of the vehicle.
If occurrence of skidding is detected during corner traveling of the vehicle on the basis of an output value from the angular velocity sensor 22, the VSC electronic control device 20 has a function to control the fuel injection amount of the engine or the ignition timing and to perform brake control to cause the vehicle to travel along the corner, thereby preventing the vehicle from being out of the traveling line and causing an accident.
The angular velocity sensor 22 is, for example, a yaw rate G sensor. The angular velocity sensor 22 uses a yaw rate detection function to detect horizontal rotation of the vehicle and uses an acceleration detection function to detect skidding of the vehicle. Thus, traveling control is appropriately performed. The acceleration detection function of the yaw rate G sensor is inferior to the acceleration detection function of the acceleration sensor 3 mounted on the airbag electronic control device, and detects an acceleration (for example, 50) to an extent such that skidding of the vehicle can be detected.
In the angular velocity sensor 22, since a vibrating body provided in the angular velocity sensor 22 vibrates in accordance with an angular velocity which is a physical characteristic, the control section detects the angular velocity on the basis of the vibration characteristic. However, if the drive frequency (high frequency band of tens of thousands of Hz) overlaps the resonance frequency of the housing of the VSC electronic control device 20, and resonance occurs when the angular velocity is detected, a signal which is output from the angular velocity sensor 22 in accordance with the physical characteristic may be amplified, and the control section which receives the signal may perform erroneous control.
Resonance with a high frequency does not occur in a soft material. Thus, a buffer material, such as rubber, is provided between the housing and the electronic substrate 25, such that the resonance frequency to be generated is suppressed and kept out of the use frequency of the sensor, thereby preventing erroneous control.
The detailed configuration will be described with reference to FIG. 3. An upper housing part 40Xa and a lower housing part 40Xb of a housing 40X which accommodates the electronic substrate 25 and is fixed to the body of the vehicle are combined with each other so as to accommodate the electronic substrate 25. The combined members are fixed by fastening screws 49X to four fixing points 44X wrapped with a buffer material 50 for holding the electronic substrate 25. The electronic substrate 25 is indirectly fixed to the housing 40X through the buffer material 50.
Although the airbag electronic control device 1 has a function to cause the airbag to inflate at the time of collision, if the airbag electronic control device is broken, the function cannot be exhibited. For this reason, the airbag electronic control device is mounted near the center of the vehicle so as to be least subject to an external impact when the vehicle collides.
The VSC electronic control device 20 on which the angular velocity sensor 22 is mounted should be mounted near the center of the vehicle so as to accurately detect rotation of the vehicle. However, since a space near the center of the vehicle is small and the airbag electronic control device 1 is mounted, it is difficult to mount the VSC electronic control device 20. When one of the VSC electronic control device 20 and the airbag electronic control device 1 is selected and mounted near the center of the vehicle, from the preferential viewpoint of securing of the safety of the passenger of the vehicle, the airbag electronic control device 1 is selected.
Thus, a method is suggested in which the angular velocity sensor is mounted on the airbag electronic control device 1 so as to input a signal from the angular velocity sensor to the VSC electronic control device 20. With this configuration, it is possible to improve the accuracy of detection of rotation of the vehicle and to prevent the airbag electronic control device 1 from being broken at the time of vehicle collision.
FIG. 4 is a general view of an airbag electronic control device 30X on which an angular velocity sensor is mounted. As shown in FIG. 5, the airbag electronic control device 30X includes an electronic substrate 31X on which an angular velocity sensor 33X and an acceleration sensor 34X are mounted at the center of the electronic substrate 31X and other electronic components, such as an arithmetic section 32X, are appropriately mounted, and a housing which accommodates the electronic substrate 31X and is fixed to the body of the vehicle.
FIG. 6 is a perspective view showing a cross-section at a position P along an XY plane in the airbag electronic control device 30X of FIG. 4. FIG. 7 is a plan view showing the cross-section at the position P along the XY plane in the airbag electronic control device 30 of FIG. 4. A housing 40X has fixing portions 41X, 42X, and 43X which are fixed to the body of the vehicle by screws. The electronic substrate 31X has fixing points 44X, 45X, 46X, and 47X for fixing to the housing 40X.
A method of combining and fixing the housing 40X and the electronic substrate 31X is as shown in FIG. 8. That is, an upper housing part 40Xa and a lower housing part 40Xc are combined with each other so as to accommodate the electronic substrate 31X, such that fixing points 44Xb, 45Xb, 46Xb, and 47Xb of the electronic substrate 31X, fixing points 44Xa, 45Xa, 46Xa, and 47Xa of the upper housing part 40Xa, and fixing points 44Xc, 45Xc, 46Xc, and 47Xc of the lower housing part 40Xc are fixed by four screws 49X.
An example of how the resonance frequency of a first trial device in which the electronic substrate 31X and the housing 40X are fixed by four fixing points having the above-described buffer material and the resonance frequency of a second trial device in which the electronic substrate 31X and the housing 40X are fixed by four normal fixing points with no buffer material are generated will be described with reference to FIG. 9.
In FIG. 9, the horizontal axis represents a vibration frequency which is given to the first trial device or the second trial device, and the vertical axis represents a level (attenuation ratio (dB)) when the first trial device or the second trial device resonates in accordance with the given vibration frequency. Data representing the resonance level in each frequency band of the first trial device is data dt1 indicated by a one-dot-chain line, and data representing the resonance level in each frequency band of the second trial device is data dt2 indicated by a solid line.
Referring to FIG. 9, data dt1 of the first trial device indicates that, as indicated by an area A, the first trial device greatly resonates with the vibration frequency equal to or lower than thousands of Hz. When this happens, since the acceleration sensor 34X uses a low frequency band equal to or lower than thousands of Hz, if the first trial device resonates in the frequency band, the airbag may be erroneously controlled. Meanwhile, data dt1 indicates that resonance is small with the vibration frequency of tens of thousands of Hz. When this happens, since the angular velocity sensor 33X uses a high frequency band of tens of thousands of Hz, there is almost no case where vehicle control is erroneously performed. That is, it is certain that the first trial device is appropriate for exhibiting the VSC function based on the angular velocity sensor 33X without causing erroneous control.
Referring to FIG. 9, data dt2 of the second trial device indicates that, as indicated by an area B, the second trial device comparatively greatly resonates with the vibration frequency of tens of thousands of Hz. When this happens, since the angular velocity sensor 33X uses a high frequency band of tens of thousands of Hz, if the second trial device resonates in the frequency band, erroneous travel control may be performed by the VSC function. Meanwhile, data dt2 indicates that resonance is small with the vibration frequency equal to or lower than thousands of Hz. When this happens, since the acceleration sensor 34X uses a low frequency band equal to or lower than thousands of Hz, there is almost no case where the airbag is erroneously controlled. That is, it is certain that the second trial device is appropriate for exhibiting an airbag control function based on the acceleration sensor 34X without causing erroneous control.
However, the resonance frequency band of the airbag electronic control device on which both of the angular velocity sensor and the acceleration sensor are mounted should be set so as not to overlap all the frequency bands which are used by the sensors.